The present invention relates to a sheet-fed rotary printing machine with a turn-over mechanism for use in both single side printing and double side printing.
To meet various printing demands, there has been proposed and practiced a variety of sheet-fed rotary printing machines with turn-over mechanisms capable of selectively effecting single side printing and double side printing. The printing machines of this type have a printing cylinder for printing one side of a sheet gripped by grippers thereon and then winding the sheet therearound, a turn-over cylinder disposed in confronting relation to the printing cylinder for gripping the printed sheet with turn-over grippers thereon and then turning over the sheet, and a next printing cylinder for effecting printing the reverse side of the sheet transferred from the turn-over cylinder. For single side printing only, the turn-over grippers remain inoperative to prevent the sheet from being turned over on the turn-over cylinder, and the sheet is transferred to the next printing cylinder so that the same first side of the sheet will be printed. The principles of the turn-over mechanism remain the same for various printing machines previously proposed. However, known printing machines have differently arranged cylinders and different turn-over machanism constructions.
Some printing machines have a single turn-over cylinder interposed between front and rear printing cylinders. However, it is general practice to use front and rear printing cylinders, a transfer cylinder having the same diameter as those of the printing cylinders, another transfer cylinder having the diameter twice those of the printing cylinders, and a turn-over cylinder of the same diameter as those of the printing cylinder. The latter type of printing machine requires more cylinders and hence is costly to install, and also needs a large space between printing units, resulting in an increased length of the printing machine. This printing machine is also disadvantageous in that the more the printing units, the larger the printing machine.
The other type of printing machine, with a single turn-over cylinder interposed between printing cylinders, is simpler in cylinder arrangement, but the construction of the turn-over mechanism is quite complex. U.S. Pat. Nos. 3,455,547 and 3,654,861 disclose such printing machines. In the disclosed printing machines, turn-over grippers are pivotably mounted on free ends of arm pivotably supported on the cylinder periphery and angularly movable by a cam link mechanism, the turn-over grippers being openable and closable by another cam link mechanism. For double side printing, the turn-over grippers are caused to revolve in response to angular movement of the arms while the grippers are being opened and closed, and the turn-over grippers are actuated by the cam link mechanism to cooperate with suction devices in gripping the trailing edge of the sheet and turning over the sheet. When single side printing is to be effected, the angular movement of the arms and the actuation of the suction devices are arrested, and the sheet is gripped successively by the grippers as they are opened and closed.
With the different cam link mechanisms provided respectively for opening and closing the turn-over grippers and for turning the arms, however, the disclosed turn-over mechanism is quite complicated in structure, hence costly, and is subjected to poor precision during operation. During double side printing, the many turn-over grippers that are heavy have to revolve around the arm shafts different from gripper shafts about which the grippers are opened and closed. Therefore, the turn-over grippers undergo a large moment of inertia, cannot grip sheet edges with precision, and present an obstacle to high-speed operation of the printing machine.